My First Tube Amp Build

[mar2112]

As the title says this is my first tube amp build. Over the years I have  built many other circuits on protoboards, wirewrapped and PCB. However, this was my first experience soldering turrets.

My Monoprice Tube15 decided to start eating power tubes. Instead of messing around with trying to troubleshoot the PCB, with it's surface mounted components, I decided to just gut it and start over.

I decided to build the Micro Bassman by Rob Robinette. Since I kept the reverb and FX loop circuitry from the Tube15 I modified Rob's layout to include ±15VDC for the Op Amps on that PCB. I also included Rob's Gain Boost, Tone Bypass and NFB mods. Pics and schematic are attached.

The build went well. Over the course of many electronic projects I've learned to double, triple and quadruple check during assembly. As such all wiring errors were caught before applying power and no smoke was released on power up.

After a few days of use I was getting some harsh sounds at higher volumes which have seemed to disappear after replacing V2. While troubleshooting this noise I noticed that if I move the wires connected to V2A Cathode and Grid I get some noise out of the speaker.

Any one have any suggestions as to why these wires are noisy?

I'd like to have an Aux In, in parallel to FX Return, so I can connect a source for backing tracks. I've looked and have not found a circuit on line. I've seen a lot of people say don't do it as it won't be Hi Fi. I don't need Hi Fi for a backing track. Is something like this doable in a tube amp?

Thanks, Michael

[dogburn]

The wiring around the tube sockets is quite busy - you might want to move the V2a wires away from other wires, like those OT wires.

[mar2112]

I should have mentioned that I did get more separation between OT wires and other wiring. The photo was taken before I did that.

I've been thinking about rerouting the OT wires on to the underside of the chassis. The easiest way to do that is to invert the OT. Otherwise the wires will have a 180° bend and those wires are a bit stiff.

[dogburn]

Also, you should probably not twist the OT wires, at least according to Rob Robinette: "Do not twist the output transformer wires, especially the primary wires that run to the power tube sockets. Twisting them together can allow capacitive coupling and the loss of high frequencies."

[mar2112]

Monoprice had them twisted so I just left them that way. I'll untwist and give it a play.

[mar2112]

I untwisted and re-routed the OT wiring outside the chassis. It was to do easier than I anticipated.

Still looking for suggestions on how to add an Aux In.

[AlNewman]

Probably have to see an as built schematic in order to suggest an Aux in.

[mar2112]

I posted the schematic in my original post.

[AlNewman]

I posted the schematic in my original post.

I see a layout and a couple pictures, no schematic.

[mar2112]

Sorry. Grabbed the wrong file in my first post.

Schematic is attached.